1. Field of the Invention
Embodiments of the present invention generally relate to a test system for substrates. More particularly, the invention relates to an integrated testing system for large area substrates in the production of flat panel displays.
2. Description of the Related Art
Flat panel displays, sometimes referred to as active matrix liquid crystal displays (LCD's), have recently become commonplace in the world as a replacement for the cathode ray tubes of the past. The LCD has several advantages over the CRT, including higher picture quality, lighter weight, lower voltage requirements, and low power consumption. The displays have many applications in computer monitors, cell phones and televisions to name but a few.
One type of active matrix LCD includes a liquid crystal material sandwiched between a thin film transistor (TFT) array substrate and a color filter substrate to form a flat panel substrate. Generally, the TFT substrate includes an array of thin film transistors, each coupled to a pixel electrode, and the color filter substrate includes different color filter portions and a common electrode. When a certain voltage is applied to a pixel electrode, an electric field is created between the pixel electrode and the common electrode, orienting the liquid crystal material to allow light to pass therethrough for that particular pixel. The substrates used typically include a large surface area and many independent flat panel displays are formed on the large area substrate, which are subsequently separated from the substrate during final manufacturing.
A part of the manufacturing process requires testing of the large area substrate to determine the operability of pixels in each flat panel display. Voltage imaging, charge sensing, and electron beam testing are some processes used to monitor and troubleshoot defects during the manufacturing process. In a typical electron beam testing process, TFT response within the pixels is monitored to provide defect information. In one example of electron beam testing, certain voltages are applied to the TFT's, and an electron beam may be directed to the individual pixel electrodes under investigation. Secondary electrons emitted from the pixel electrode area are sensed to determine the TFT voltages.
Generally, a test apparatus, such as a prober assembly, is used to apply or sense voltages from the TFT's by contacting conductive areas on the large area substrate. The prober assembly is sized and adapted to test a specific configuration of flat panel displays laid out on the substrate. The prober assembly typically has an area sized equal to or greater than the dimensions of the substrate, and this large area of the prober assembly creates handling, transfer, and storage challenges.
Therefore, there is a need for a prober assembly to perform testing on large area substrates that addresses some of the challenges discussed above.